This invention relates to plant for use in carrying out the separation of the impurity content of impure water by the immiscible refrigerant freeze process. The said process broadly comprises boiling the immiscible refrigerant in impure water to be processed, separating the ice crystals formed and melting the ice crystals to produce water purified to an acceptably low inorganic salt concentration. A plant for the said process must comprise a plurality of plant components each carrying out one or more process steps and thus provision must be made for transferring process materials between one component and the next. In attempting to reduce capital costs, designers' attention has been directed to the formulation of an integral design of plant so avoiding the need to duct process fluids between spaced apart plant components and at the same time easing thermal insulation problems. However this integral concept has not so far been achieved without compromising to some degree the operational efficiency of one or other of the plant components to the detriment of overall performance. This is a disincentive to integrate for, in plant of this kind, there is a definite relationship between the outline shape of a conventionally designed plant component and its efficient functioning which imposes constraints on the ultimate outline which the plant may assume.
The present invention aims to produce an integrated plant which compromises little, if at all, with operational efficiency.
Considering now the specific plant components of an immiscible refrigerant freeze separation plant, these comprise a crystalliser in which ice crystals are formed in the liquid to be treated by boiling in it a liquid refrigerant, a wash column in which an ice column is formed from compacted ice crystals, a condenser/melter in which refrigerant vapour is condensed in melting compacted ice scraped from the top of the ice column and a decanter in which the condensed refrigerant separates from the product water and is poured off the top of underlying water. Thus, whilst the wash column and condenser/melter are vertically orientated plant components which may be reasonably evenly matched in height, the crystalliser must be strictly limited in height. In practice; too deep a fluid flow in the crystalliser does not allow the secondary refrigerant liquid to evaporate on injection into the impure liquid due to the latter's hydrostatic head unless a very low refrigerant inlet pressure is to be employed. The decanter also tends towards a horizontal axis so that the fluids may lose velocity, separate and the less dense liquid may be decanted successfully.